Images are often shot on photographic film. The images may be displayed from the film, such as direct projection of motion picture film in a theater. Also, images on film are converted from film to an electronic medium, such as videotape, which is then used for mass distribution or broadcast via television or cable.
Conventionally, motion picture film is converted to an electronic medium by a telecine. The most widely available telecines utilize a flying spot scanner to scan each image of the film. As shown in FIG. 1 and FIG. 2, movie film 10 is scanned in a raster pattern 12. Light from a CRT 14 is focused via lenses 16 onto one or more photo cells 18 after having passed through the film 10. The output of the photo cell 18 constitutes an electronic signal whose intensity corresponds to the progressive scan of the movie film 10. Optionally, a color corrector 20 may vary the electronic signal of the colors as is known in the art. Ordinarily, the output of the telecine is stored in memory. Conventionally, a frame store memory 22 stores a digital version of the image. As necessary, an analog to digital converter 24 is used if the output of the telecine or color corrector is analog.
Current television displays use an interlaced display system. A first field for display on a television will utilize the first, third, fifth and so on, scans from the raster 12, and the second field will use the second, fourth, sixth and so on lines of the raster 12. By storing the progressive scan from the telecine in the frame store memory 22, the interlaced output may be achieved by sequentially addressing the memory 22 for the desired lines. The output from the memory 22 may be either digital video output 26 or, after passing through a digital to analog converter 28, an analog video output 30. The write address generator 32 for the memory 22 generally will sequentially record the raster scan 12. The read address generator 34 will read data from memory 22 in the selected format, such as the interlaced format.
In motion pictures, the aspect ratio (that is, the ratio of the width to the height of the image) is larger than for most current television sets. Motion pictures are often shot in cinemascope format which has an aspect ratio of 2.35:1. Conventional television sets have an aspect ratio of 1.33:1 (4/3). When shooting motion picture film, a special 2:1 anamorphic lens is often used to compress the image onto conventional sized film. Such a 2:1 anamorphic lens results in a 1.175 aspect ratio. Inspection of the film shows images which are squeezed by a factor of 2:1. By way of example, people appear very tall and very thin. When anamorphic film is replayed in the theater, a projection lens expands the picture to the correct proportions.
When a telecine is used to scan ordinary film for a 1.33:1 aspect ratio, the scan is as shown in FIG. 3a. While literally hundreds of lines are used to scan a single image on a film, for simplicity the image in FIG. 3a shows 28 lines. A scan of film for use in a 1.33:1 aspect ratio display would use lines 1-20 written to the memory 22. As each sequential line is scanned, it is stored in memory 22 at the write address specified by write address generator 32. Extra CRT scan lines are typically present, and are shown above and below scan lines 1-20.
Telecines ordinarily, do not utilize an anamorphic lens. Thus, when scanning images recorded with an anamorphic lens, some correction must be made, lest the images appear in their squeezed form. The conventional solution has been to double the vertical raster height of the flying spot scanner 8. FIG. 3b shows the raster scan when expanded by 2:1 in the vertical direction. When scanning an image area of cinemascope film having a 1.18:1 aspect ratio, lines 5-16 (shown bracketed) would be used. By doubling the scan distance, the image is converted back to its normal proportions. However, when the scanned image is then displayed on a television having a 1.33:1 aspect ratio, the image fills only a portion of the screen 40 (FIG. 4). The portions outside the image area 42 are blanked, and appear black. This display is known as a “letterbox” display.
FIG. 3c shows the video output from the memory for the letterbox format. Lines 1-4 and 17-20 will be blanked. For output in the interlaced format, lines 5, 7, 9, and so on would be output in the first frame, and lines 6, 8, 10 and so on would be output in the second frame.
There have been long standing and vexing problems to the image quality utilizing the above described technique and apparatus. The first problem is that a moire pattern, that is, the type of image often seen when two geometrically regular patterns (as when two sets of parallel lines are superimposed especially at an acute angle) may show up on the video image. This is especially pronounced where numerous horizontal lines are shown in the image, bleachers, car grills or certain fabrics. By way of example, as a image pans across bleachers, a moire pattern may travel over the bleachers, clearly creating an image which would not be observed by someone at the actual scene. This lack of realistic representation on video has been a serious problem.
The second problem occurs if the scanning spacing on the telecine matches a spacing on the image. In this event, when an interlaced display is utilized, the image visibly flickers. To consider an extreme example, if the image consisted of alternating horizontal black lines on a white background, and if the telecine scan were such that the odd numbered raster scans were all black and the even numbered raster scans were all white, when played back, because of interlacing, the image would be alternately all black and all white, causing a serious flicker problem.
Yet a third problem resulting from the scanning method utilized in the prior art is that the image quality of the video is visibly degraded. This results from the use of a twice as wide scan, wherein substantial detail may be omitted from the image.
Despite the long standing and vexing nature of these problems, no satisfactory solution has been proposed heretofore.